EFFECTS OF INTERTRIAL REINFORCERS ON SELF-CONTROL CHOICE

In three experiments, pigeons chose between a small amount of food del ivered after a short delay and a larger amount delivered after a longe r delay. A discrete-trial adjusting-delay procedure was used to estima te indifference points-pairs of delay-amount combinations that were ch osen about equally often. In Experiment 1, when additional reinforcers were available during intertrial intervals on a variable-interval sch edule, preference for the smaller, more immediate reinforcer increased . Experiment 2 found that this shift in preference occurred partly bec ause the variable-interval schedule started sooner after the smaller, more immediate reinforcer, but there was still a small shift in prefer ence when the durations and temporal locations of the variable-interva l schedules were identical for both alternatives. Experiment 3 found g reater increases in preference for the smaller, more immediate reinfor cer with a variable-interval 15-s schedule than with a variable-interv al 90-s schedule. The results were generally consistent with a model t hat states that the impact of any event that follows a choice response declines according to a hyperbolic function with increasing time sinc e the moment of choice.